Interpretive Summary: Wheat straw contains 65% carbohydrates that can be used for production of fuel ethanol. Generally, three steps are involved for its conversion to ethanol: pretreatment, enzymatic hydrolysis and fermentation. Integration of these process steps is important to lower the cost of production of ethanol from wheat straw. In this research, we have used a conventional yeast strain for fermentation to ethanol and combined the enzymatic hydrolysis and fermentation steps typically known as simultaneous saccharification and fermentation (SSF). We demonstrated that SSF offered distinct advantage over separate hydrolysis and fermentation (SHF) with respect to reducing total time required to produce ethanol from pretreated wheat straw by more than 50%. We showed for the first time that shifting the pH of fermentation enhances the fermentation of non-detoxified wheat straw hydrolyzate by the yeast. This finding is very important and encouraging for further development of a commercially viable biomass to ethanol fermentation process.

Technical Abstract:
Ethanol production by Saccharomyces cerevisiae NRRL Y- 2034 from wheat straw (WS) by separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) was studied. The yield of glucose from dilute acid pretreated WS (86 g L-1) after enzymatic saccharification was 26.9±0.1 g L-1. The pretreated WS was biologically conditioned to remove inhibitors by growing Coniochaeta ligniaria NRRL 30616 aerobically in the liquid portion for 15 h. The yeast produced 13.2±0.2 g ethanol per L in 94 h from non-detoxified WS hydrolysate (WSH) at pH 5.5 and 37 oC. It produced 13.3±0.0 g ethanol per L in 30 h from the biodetoxified WSH by SHF. In SSF experiments, the strain produced 13.0±0.7 g ethanol per L in 72 h from the non-detoxified WS but took 48 h to produce 13.1±0.1 g ethanol per L from biodetoxified WS. By comparison, fermentation of washed solid residues yielded 12.6±0.4 g ethanol per L in 43 h. SSF offered advantage over SHF in reducing the total time of conversion of pretreated WS to ethanol by 53-57%.